have an axe to grind idiom
想说服别人;想争个对错
to have a strong personal opinion about something that you want people to accept and that is the reason why you do something
Environmentalists have no political axe to grind - they just want to save the planet. 环境保护主义者并非想在政治上争个对错——他们仅仅想拯救这个星球而已。